This invention relates to traffic radar detection and more specifically to down-the-road Doppler radar detection.
In Doppler radar systems and particularly in down-the-road Doppler radar systems, where the axis of the antenna is directed along the line of travel of a target, there are two basic shortcomings with both enforcement and compliance with vehicle speed regulations. First, down-the-road Doppler radar systems are highly susceptible to improper target identification. Furthermore, Doppler radars are also highly susceptible to spurious target-speed readings. A Doppler radar's range typically exceeds 800 meters with a half-power beamwidth of 0.21 to 0.31 radian, substantially more than the cross-sectional area of a vehicle. As a consequence, the radar operator must make a manual determination with a high degree of uncertainty as to the identity of the target vehicle.
The problem of spurious speed readings is a phenomenon of electromagnetic and electromechanical interference effects from common sources, generally from AM or FM transmitters operating in or near the seeker source, including a seeker vehicle's own ignition system, ventilation equipment or the like. While vehicle radar detectors are in widespread use, conventional radar detectors are themselves subject to false responses due to spurious signals.
One way to safeguard a targeted object against the potential shortcomings of Doppler radar is to attempt to defeat echoes or reflections of a seeker radar signal directed at the target. In connection with general countermeasures, such as used in military applications, two active approaches have been suggested: barrage jamming and spot jamming. Barrage jamming has been used in surface vehicle applications, albeit unsuccessfully. It is not known whether spot jamming has ever been used in surface vehicle applications. In barrage jamming, a transmit-only barrage signal spreads countermeasure energy substantially continuously over a bandwidth deemed sufficiently wide to include all possible seeker frequencies in order to mask target echoes. Such an approach presupposes the availability of substantial power, with that power spread over a substantial bandwidth. The barrage method is necessarily wasteful of energy and inhibits or even prevents detection of the presence of a seeker signal.
Alternatively, a spot signal has been used where the operating frequency of the seeker signal was known or could be tracked. If the seeker signal is diverse, or if the exact frequency is not precisely known, there is a need to resort to a look-through scheme wherein a targeted receiver scans to locate an intruding seeker signal and thereafter causes energy to be transmitted on the specific frequency. Such a scheme is limited by the required time to acquire the seeker signal versus the seeker's dwell time at a given frequency and to generate a countermeasure signal at the same frequency. The sophistication of systems to perform such a task is often so costly that cost outweighs the value of the countermeasure. What is needed is a low-cost, effective and efficient countermeasure suitable for general use and which minimizes false positive responses to a seeker system while encouraging compliance of the target with vehicle operating regulations.